Recently, extended applications of magnetic particles as marker materials in a biosensing field have been variously studied. In this regards, Japanese Patent (Laid Open) No. 2006-88131 (Patent Literature 1) already filed by the same applicant discloses polymer magnetic particles with high dispersibility required for markers while keeping magnetic response properties of magnetic particles. As further developments, Japanese Patent (Laid Open) No. 2008-127454 (Patent Literature 2) already filed by the same applicant discloses multi-functional polymer magnetic particles having a function as a fluorescent marker and the magnetic response performance by incorporating fluorescent molecules within the polymer layer covering the magnetic particle. Now for the polymer magnetic particles containing fluorescent molecule, introduction of much fluorescent molecules to the coating polymer layer may be desired so as to realize fluorescence luminance detectable by a known fluorescence detector.